A function of a servo system for longitudinal tape, such as magnetic tape, is to acquire a desired servo track and move a head laterally of the longitudinal tape to accurately follow the lateral movement of the tape, for example, during read/write operations of the head. If done accurately, data tracks are written and read in straight lines along the longitudinal tape as the tape is moved in the longitudinal direction. With respect to magnetic tape, the data comprises parallel tracks in the longitudinal direction of the magnetic tape. Servo tracks are prerecorded in the magnetic tape parallel to, and offset from, the expected data tracks.
Servo systems often employ compound actuators to move the head laterally both for track following, and to shift from one servo track (or set of servo tracks) to another and thereby follow a different set of data tracks. A compound actuator, which comprises a coarse actuator and a fine actuator mounted on the coarse actuator, provides both a large working dynamic range and high bandwidth. The high bandwidth fine actuator typically has a limited range of travel to attain the high bandwidth, and the coarse actuator has a greater range of travel.
Tape guides on either side of the head have in the past had flanges to constrain the lateral movement of the tape. The flanges of the tape guides, such as rollers, limit the lateral motion of the tape, but may tend to flex the edges of the tape and to introduce debris accumulation at the flanges that impact the lifetime of the tape and in addition create undesirable dynamic effects.
Flangeless tape guides tend to solve the problems of the flanged tape guides, but, without being constrained, the longitudinal tape tends to rapidly shift from one side of the tape guides to the other, and to run at one side of the guides for a period of time and then shift to the other side.
The fine actuator is designed to handle the rapid shifts of the longitudinal tape once the servo track has been acquired, and, as such, is capable of rapidly jumping in the direction needed follow the acquired servo track. With the shifting behavior of the tape, the servo system must first find and acquire the servo track in order to follow the servo track.